Why did the Nephites offer sacrifice and burnt offerings?

Under the law of Moses, firstlings of the flock were dedicated to the Lord (Exodus 13:12, 15) and were to be brought to the temple where they could be sacrificed. A portion was thereafter, given to the temple priests to be eaten (Leviticus 17:8-9; Numbers 18:17; Deuteronomy 12:17-18; 15:19-20). Firstlings were sacrificed, but apparently not offered as the ola or burnt offering which was consumed in its entirety upon the altar (Leviticus 1:9, 13). Rather than suggests that they were used as burnt offerings, the verse suggests that the Nephites at this time brought firstlings to the temple to be sacrificed as required, and also brought other unspecified animals for burnt offerings.